EFFECT OF NITROUS-OXIDE ON VISUAL, AUDITORY AND SOMATOSENSORY EVOKED-POTENTIALS

The effects of 10, 30 and 50% N2O on visual, auditory and somatosensory evoked potentials were studied in 7 healthy volunteers. The evoked potentials were averaged from the EEG following repeated peripheral sensory stimulation of the appropriate modality. Latencies and amplitudes of the resulting potentials were measured and compared with control values. In 5 subjects, increasing N2O concentrations were associated with a graded reduction in amplitude of the visual (P < 0.02) and somatosensory (P < 0.02) evoked potentials. The latency of the 1st major negative potential of the visual evoked potential was significantly increased (P < 0.02). Latencies of brainstem auditory evoked potentials did not alter. In the other 2 subjects the amplitude of the visual and somatosensory evoked potentials showed graded increase with decreasing concentrations of N2O, confirming that the changes are dose related. As N2O is used almost universally during anesthesia, these changes must be taken into account when assessing variations observed during operation in anesthetic-related evoked potential studies.